Process for forming a peelable seal

ABSTRACT

A process for forming a peelable seal by heat sealing under combined application of heat and pressure at least two polyolefin film members having at least one oxidized surface therebetween, and the seal formed thereby.

This is a continuation of application Ser. No. 830,051 filed Sept. 2,1977 now U.S. Pat. No. 4,183,434.

BRIEF DESCRIPTION OF THE INVENTION

This invention relates to a peelable seal for use in connection withcontainers and to a process for producing the same.

DISCUSSION OF THE PRIOR ART

It is well known in the art to utilize plastic bag containers inpackaging because of their low cost and ease in manufacture. The plasticbag containers have found their use in packaging frozen foods, tobacco,hardware, medicaments, articles of manufacture, as boilable cookingbags, and the like. At the present time, various methods are utilized toseal the container either at a time prior to filling so as to maintainits integrity or after filling with the desired product. The sealing ofthe container takes place by various methods such as weld sealing withheat and/or pressure, utilizing various adhesives, etc. Such sealing ofthe container provides a disadvantage in that separation without tearingor particle formation is difficult and re-sealing when necessary is notpossible in all cases without additional equipment or sealingcomponents. There are many applications wherein a peelable seal on thecontainer is most advantageous. Until now, only polyvinyl chloride filmhas been commercially utilized to form a container having a peelableseal of a plastic material. The utilization of the polyvinyl chloridefilm has been found to be disadvantageous wherein human consumption ofthe contained product takes place due to the fact that there is aleaching out of certain chemicals from the film into the product whichare harmful when the product is consumed by humans. Additionally,polyvinyl chloride has the disadvantage of requiring additionalingredients to form the seal or when opened leaves a residue about thepeeled area which can cause contamination.

U.S. Pat. No. 3,081,214 to Thomas Henry Strome discloses the surfacetreatment of polyethylene with corona discharge in order to activatepolyethylene film so as to provide a strong bond with inks having anitrocellulose or polyamide base.

U.S. Pat. No. 3,360,412 to Albert L. James discloses a process forproducing a heat seal lamination from a film of polyolefin materialwhich has been pretreated with electrical corona discharge or anoxidizing gas flame. Under the conditions disclosed in this patent, asubstrate web is heated to a temperature at least equal to the fusiontemperature of the thermoplastic film so that there is formed apermanent bond.

U.S. Pat. No. 3,491,935 to Claude H. Trotter, Jr., et al discloses theformation of a peelable seal utilizing the principle of differentialfusion between certain thermoplastic material by using heat input.

U.S. Pat. No. 3,914,521 to Theodore R. Beatty et al relates to aheat-treated, corona-treated polymer body having a surface susceptibleto adhering to adhesives or the like in order to form a strong permanentbond. Thus, it is known in the art that subjecting a polymer film to acorona discharge using an energy of up to 1-4 watts-min/sq.ft., canincrease the surface adhesion characteristics for the film. There isfurther shown a specimen of polypropylene film which was subjected to acorona treatment using a 2 kilowatt Union Carbide corona dischargedevice which was set to impart an energy density-to-film surface of 118watts-min/sq.ft. to the film. The corona discharge lasted approximatelyten seconds after which a scanning electron microscope was used toobtain a photomicrograph of the corona-treated film wherein the surfacethere was found to contain a definite gathering of crystals withdistinct crevices formed between adjacent crystals.

It is known to produce a peelable seal on containers formed from plasticmaterial by applying only a slight pressure during heat sealing.However, such prior art methods require precision and controlled heatsealing operations which prevent the commercialization of the method.Furthermore, such sealing is inconsistent and not reliable.

Although various methods have been composed to provide a flexibleplastic container with a peelable seal utilizing an inert plasticsubstance, none have resulted in a container which can be utilized bothat a low temperature and at a high temperature.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a container with apeelable seal which overcomes the disadvantages of the prior art, andwhich provides for an application together with non-plastic componentsof a container.

It is a further object of this invention to provide a container whichutilizes a seal formed only of the containers' components and withoutthe use of additional ingredients.

SUMMARY OF THE INVENTION

The present invention relates to a method for treating a polyolefin filmthat is utilized in the formation of containers so as to render thecontainer with a peelable seal. More particularly, the present inventionrelates to the treatment of a polyolefin film which in itself forms acontainer or where the polyolefin is utilized in combination with othermaterials such as other plastics or metal.

It has now been found that polyolefin films can be made to form apeelable seal if at least one film surface is oxidized by either anapplication of an open flame which is an oxidizing flame such as apropane flame or corona discharge. The latter may be applied under theconditions disclosed by R. M. Sonkin in "Corona-Discharge Treatment ofPolyolefin Films", Plastics Engineering, February, 1977, pages 50-52prior to heat sealing.

According to the method of sonkin, polyolefin film is passed over adielectric-covered treater roll where it is exposed to a continuousplasma of ionized particles (corona) from an electrode. The coronatreatment of the polymer results from the bombardment and penetration ofthese ions into the molecular structure at the surface of the material.It is believed that the oxidation and polar group formation in thesurface molecules induces the rise in surface tension of the treatedmaterial. Thus, the corona treatment alters the film surface,principally by oxidation, to change the surface polarity, andconsequently, the surface tension.

The oxidized surface results in an interface which resists fusion of thefilm during controlled heat sealing.

The interface is a result of the gathering of crystals or spherulitesalong the film surface as shown in U.S. Pat. No. 3,914,521. It is thepresence of the interface which resists the formation of the fusion bondunder the conditions set forth by the prior art for non-treated film.Heat sealing the treated polyolefin utilizing combined temperature andpressure conditions provides a complete seal which is not fusion bondedand is peelable. As the temperature and pressure conditions increase inthe heat sealing operation, the bond increases in strength until therereaches a point that fusion occurs as contemplated by the prior art toform a weld seal.

The test to determine the presence of a suitable interface may be madepursuant to the wettability test set forth by A. J. G. Allen in "TheSpreading of Liquids on Polyethylene Film: The Effect of Pre-PrintingTreatments", 132nd National Meeting, A. C. S., New York, Sept. 8-13,1957 (17 No. 2).

A peelable seal is formed when polyolefin films are heat sealed togetherunder a controlled application of temperature and pressure with at leastone of the surfaces between the films being oxidized. Generally, atreated polyolefin film having a surface energy of 30-50 dynes/cm. issubjected to a pressure of 500-1500 lbs/sq.in. of sealing area at atemperature of about 200°-500° F. The dwell time of the application ofthe pressure is well known in the art as noted in U.S. Pat. No.3,491,935 of Trotter et al and is dependent upon factors such as film,thickness and peel strength desired. Prolonged application of pressure,higher temperatures and increased pressures would result in a weld seal.

It is understood that the term "heat sealing" as used herein refers tothe technique of sealing by the heat and pressure together.

The utilization of a polyolefin has been found to be very advantageousfor making bags because of its inertness to various feeds and chemicals.Furthermore, polyolefin containers are known to be capable of use asboilable containers and for storing frozen products.

Other objects and advantageous of this invention will become furtherapparent hereinafter, and in the drawing of which:

DRAWINGS

FIG. 1 is a diagrammatic representation of a process for producing acontainer with a peelable seal according to the present invention;

FIG. 2 illustrates a polyolefin bag containing a peelable seal on oneside;

FIG. 3 illustrates a polyolefin bag containing several peelable portionsof different strength;

FIG. 4 illustrates the application of the present invention to acontainer formed in combination with other materials;

FIG. 5 illustrates the application of the present invention to adispensing container for medicaments, and

FIG. 6 illustrates the application of the present invention to a bloodstorage bag.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates one method of forming flexible containers withpeelable seals in accordance with the present invention. Polyolefin filmis fed from supply rolls 10, 10' and is oxidized on a surface beingsubjected to corona discharge by lamps 12, 12'. The treated films arethen passed through rolls 14, 14' end into a platen press 16 wherein thesealing occurs utilizing selected temperatures and pressures whichdepends upon the particular density of the polyolefin utilized and thedesired permanency or peelability of the seal. The individual containersare then cut from the rolls by means of a cutter 18.

In lieu of corona treatment, the surfaces of the polyolefin film may beoxidized utilizing an open flame. Typically, the treated polyolefin filmhas a surface energy of 30-50 dynes/cm. The sealing pressure exerted bythe platen press is generally 500-1500 lbs. per square inch of sealingarea and sealing is conducted at a temperature of about 200°-500° F.Besides the use of a platen press, forming rolls may be utilized in theconventional method of producing plastic containers. Also, it has beenfound to be advantageous to form the polyethylene containers utilizingimpulse sealing techniques.

It can be readily seen that the treated polyolefin can be utilized toform containers having a wide variety of uses. As shown in FIG. 2, apolypropylene bag 30 is formed wherein there is a permanent seal 32along the edge on three sides only with the remaining portion having apeelable seal 36 so that upon the application of a peeling force bymeans of free end flaps or tabs 38, 38', the peelable seal 36 is peeledapart so as to provide access into the container. Such a container issuitable for use when the container's integrity is to be maintainedprior to filling with an article such as food.

In FIG. 3 there is shown a polyethylene container 40 which is providedwith a plurality of compartments 44a, 44b, 44c that are formed by meansof seals 46a, 46b, 46c, 46d. Each of the seals 46a, 46b, 46c, 46d has adifferent peel strength. Free ends 48, 48' serve as gripping means forpeeling apart the seal 46a. Container 40 is especially adaptable forutilization as a mixing bag wherein the contents of the container are tobe kept separated and mixed only prior to use, such as in the case withepoxy cements.

FIG. 4 shows the utilization of a peelable seal 56 in connection with ametallic can 50 having a metallic body portion 52 and a treatedpolyethylene lid 54.

FIG. 5 illustrates the adaptability of the peelable seal 61 for use inpackaging such articles as medicaments 62 wherein individualcompartments are formed in the container 60 so as to permit easy accesswhen required by peeling the edges of each compartment by theapplication of a peeling force with free end tabs 63, 63'. Thecompartments may be formed by the selective heat sealing of two films oralternately, by heat sealing a plurality of films over a single film.

Turning now to FIG. 6, there is shown a sterilizable, flexiblepolyethylene bag 70 with holes 71 for hanging the bag either in anupright or in an inverted position. Bag 70 also includes a first hollowoutward protrusion 77, welded onto said bag, a second hollow outwardprotrusion 78 such as for use in introducing plasma into the bag, and athird hollow protrusion 79, such as for introducing platelets into thebag, formed at the upper periphery of the bag. Along the periphery ofthe bag is provided a weld seal 74. Further, each protrusion 77, 78 and79 is provided with a protective closure which forms a bag and isprovided with tabs 73, 73'. Each of the bag portions over theprotrusions is formed by means of a weld seal 74 at its base and by apeelable seal between the base portion and the tab or free end portions73, 73'. The tab portions 73, 73' serve as a gripping means for openingthe peelable seals.

It has been further found to be advantageous to provide a peelable sealin a platelet bag close to the plasma inlet 78 and platelet inlet 79, asillustrated by peelable seals 76a, 76a' and 76b, 76b'. By providing theseal close to the tubes 78 and 79, air pressure is created whichprevents the occurrence of flow due to capillary action in an unusedinlet 78 or 79 when only one of the inlets 78 or 79 is utilized.Optionally, after utilization, the bag may be re-sealed below theinlets. Also, to prevent flow of bag contents into tube 77, apuncturable membrane 80 is provided.

An advantage of the present blood storage bag also lies in that plasticsheets of the same material and thickness are used for both the bag andthe protective closure; the seal is unfailingly peeled open and thejunction between the protective closure and the seal around the inlets78, 79 act as a stopper.

In connection with maintaining sterility, since the protective closureis peeled in the way described, there is little possibility that germssticking to the tab or protective closure can fall into the adjacentport as the tab is turned over. Also, with the peelable seal theintegrity of the seal is insured until the bag is utilized.

The ports may also include a ridge or spherical enlargement on its outerdiameter so as to provide a convenient and simple means for adapting thebag to any of a variety of blood storage applications, including thestorage of various blood components and the freeze storage of red bloodcells.

It is understood that the present invention may be utilized inconnection with other blood pack systems such as in the collection,preparation, storage or administration of whole blood or bloodcomponents.

It is further understood that the term "weld seal" as used herein refersto either a peelable seal of high strength or a weld seal.

While this invention has been described with respect to specificembodiments thereof, it should be understood that this invention is notlimited to those embodiments and that the appended claims are intendedto include these and other features and embodiments as may be devised bythose skilled in the art which are nevertheless within the spirit andscope of this invention.

I claim:
 1. In a process for forming a peelable seal with at least twoextruded polyolefin film members by the simultaneous application ofcontrolled heat and pressure to said film members at the portion to besealed, the improvement which comprises oxidizing by corona dischargetreatment at least one surface of at least one of the polyolefin filmmembers at the portion to be sealed so as to modify by oxidation thestructure of the surface crystals formed by extrusion and thensimultaneously applying controlled heat and pressure to soften themodified crystals at the contacting surface to partially fuse thecrystals at the contacting surface while maintaining the integrity ofthe crystals so that the modified crystals form an interface between thepolyolefin film members at the seal portion and a peelable seal isthereby formed.
 2. A process according to claim 1 wherein at least twopolyolefin film members having a surface oxidized by corona dischargetreatment are sealed together so that the oxidized surface of each filmmember forms the interface therebetween.
 3. The process according toclaim 1 wherein said polyolefin is polyethylene.
 4. The processaccording to claim 1 wherein said polyolefin film members are peelablysealed across the opening of a container.
 5. The process according toclaim 1, wherein a portion of said oxidized polyolefin film members areheat sealed to form a peelable seal and another portion of said oxidizedpolyolefin film members are heat sealed to said surface so as to form aweld seal.
 6. The process according to claim 1, wherein said treatedpolyolefin film members are subjected to pressure between 500-1500 psiof sealing area and sealing is conducted at a temperature of about200°-500° F.
 7. The process according to claim 1, wherein said treatedpolyolefin film members are heat sealed at selective portions so as toform compartments.